1. Field of the Invention
The present invention relates to a tank and a method for storing an easily polymerizable compound. More particularly, the invention pertains to a tank for storing an easily polymerizable compound, such as a (meth)acrylic acid, and a method for storing the easily polymerizable compound using the tank, in which polymerization of the compound is inhibited or substantially retarded to enable stable storage thereof.
2. Description of the Prior Art
When storing an easily polymerizable compound, such as a (meth)acrylic acid, it is commonly practiced to add a polymerization inhibitor, such as hydroquinone or phenothiazine, or introduce inert gas containing molecular oxygen into a storage tank to prevent polymerization of the compound. Another conventional approach to prevent polymerization is to cool and circulate a polymerizable compound to regulate its temperature within a storage tank or to make the concentration of a polymerization inhibitor uniform within the polymerizable compound.
Even if such methods of preventing polymerization are used, however, the polymerization inevitably would occur, and it has been impossible to store an easily polymerizable compound in a stable fashion due to adhesion of a polymer or clogging of a flow channel (circulating pipe) by the polymer, making it necessary to chemically or manually remove the adhering or clogging product at regular intervals. It has therefore been an important issue to prevent polymerization within a storage tank for storing an easily polymerizable compound.
Generally, in a storage tank, a liquid taken from a production process is stored in the tank and drawn therefrom for shipment as a commercial product or for use in another production process whenever the need arises. When the stored liquid is an easily polymerizable compound, a polymerization inhibitor is added to the product to prevent its polymerization as described above. In this case, it is preferable that the concentration of the polymerization inhibitor within the polymerizable compound in the storage tank and within the polymerizable compound drawn from the storage tank be kept as uniform as possible. In other words, it is preferable that the polymerizable compound having as uniform a composition as possible can be drawn from the tank.
The invention provides a tank for storing an easily polymerizable compound, the tank fitted with a liquid inlet pipe, a liquid draw-off pipe and a liquid recirculating pipe, wherein the liquid inlet pipe and/or the liquid recirculating pipe is arranged in such a position with respect to the liquid draw-off pipe that, assuming that terminal ends of the invididual pipes are located at the same height (i.e., when viewed from above, so that height is not a consideration as to whether lines intersect with each other), the apex angle of a triangle formed by a line joining the central points of both end openings of the liquid inlet pipe and the liquid draw-off pipe and the point of intersection of horizontal lines extended individually from the central points of the end openings of the liquid inlet pipe and the liquid draw-off pipe to the central point of a horizontal cross section of the tank, or the apex angle of a triangle formed by a line joining the central points of both end openings of the liquid recirculating pipe and the liquid draw-off pipe and the point of intersection of horizontal lines extended individually from the central points of the end openings of the liquid recirculating pipe and the liquid draw-off pipe to the central point of the horizontal cross section of the tank, is equal to or larger than 90xc2x0.
The invention also provides a method of storing an easily polymerizable compound by use of the tank as defined above.